1. Field of the Invention
The present invention relates to a thermoplastic polyurethane composition comprising a thermoplastic polyurethane and an ethylene-vinyl alcohol copolymer and/or a polyamide.
2. Description of the Related Art
A thermoplastic polyurethane has been widely used because it is excellent in various properties such as mechanical strength, flexibility, elastic recovery from strain and abrasion resistance. A film, a sheet, a belt, a hose, a tube and other various articles may be produced with a thermoplastic polyurethane by extrusion molding or injection molding.
An article, made of a thermoplastic polyurethane and having good gas barrier property, has been required. For example, multi-layered structures having a layer of a thermoplastic polyurethane and a layer of an ethylene-vinyl alcohol copolymer or a polyamide, each of which is known as a polymer having excellent gas barrier property, are proposed [see Japanese Patent Application Laid-open Nos. 22163/1983 (JPA 58-022163), 258341/1990 (JPA 2-258341), 5143/1991 (JPA 3-005143) and 110154/1998 (JPA 10-110154)].
A process for producing an article made of a thermoplastic polyurethane and an ethylene-vinyl alcohol copolymer or a polyamide inevitably causes a scrap such as(i) a lug of a film which is involved by co-extrusion process, (ii) trimmings which is involved by co-extrusion blow molding process and (iii) defective moldings. It is desirable to reuse such a scrap from the viewpoint of production cost and resource saving.
In addition, it is also desirable to recycle an article made of a thermoplastic polyurethane and an ethylene-vinyl alcohol copolymer or a polyamide.
Various attempts have been applied for the recycle of an article made of an ethylene-vinyl alcohol copolymer. For example, Japanese Patent Application Laid-open No. 195635/1995 (JPA 7-195635) discloses a method for the recycle of a multi-layered structure having a layer of an ethylene-vinyl alcohol copolymer and a layer of a polyolefin. Also, U.S. Pat. No. 6,294,602 and Japanese Patent Application Laid-open No. 248073/2000 (JPA 2000-248073) disclose a method for the recycle of an article made of a polymer composition comprising an ethylene-vinyl alcohol copolymer, a polyamide and a copolymer of an olefin and an unsaturated carboxylic acid. However, these documents are silent with a method for the recycle of an article made of an ethylene-vinyl alcohol copolymer and a thermoplastic polyurethane.
A thermoplastic polyurethane composition comprising a thermoplastic polyurethane and an ethylene-vinyl alcohol copolymer and/or a polyamide may be formulated by melting [i] an article made of a thermoplastic polyurethane and an ethylene-vinyl alcohol copolymer and/or a polyamide or [ii] a scrap involved by a process for producing an article made of a thermoplastic polyurethane and an ethylene-vinyl alcohol copolymer and/or a polyamide. However, in most cases, a combined use of a thermoplastic polyurethane and an ethylene-vinyl alcohol copolymer and/or a polyamide tends to cause gelation upon melt molding.
Japanese Patent Application Laid-open Nos. 206634/1990 (JPA 2-206634) and 255288/1991 (JPA 3-255288) disclose a uniform thermoplastic polyurethane composition, which can be formulated without gelation, comprising a thermoplastic polyurethane and an ethylene-vinyl alcohol copolymer having specific ethylene content. Japanese Patent Application Laid-open No. 324162/1995 (JPA 7-324162) also discloses a polymer composition comprising a thermoplastic polyurethane dispersed in a matrix of a polyamide. The present inventors have found that, even with such a uniform composition, gelation may proceed at a molten state to cause a reduction of melt tension of the composition, which leads to lesser processability upon extrusion molding or injection molding.